The invention of the wheel greatly revolutionized the transportation of persons and materials. As will be appreciated, wheels must have brakes or a means to cease the rotation of the wheel to stop the movement of the vehicle to which they are attached. With vehicles powered manually, such as strollers, carts, stretchers, and the like, the provision of braking mechanisms poses unique challenges. As will be appreciated, without a braking mechanism, these vehicles cannot be left unattended on slopes or non-flat surfaces in view of the fact that the force of gravity will induce the wheels (and thus the vehicle) to roll in the descending direction. This problem is a particular concern with manually or arm-powered devices, such as wheelchairs, for example, where the safety of an occupant is of utmost importance.
As will be appreciated, caregivers attending to a wheelchair occupant sometimes need to leave the occupant unattended to, for example, open a door or prepare a car lift. In these periods, the occupant may need to prevent the wheelchair from descending an incline, or from undergoing what is know in the art as a “rollback.” Some occupants do not have the stamina, strength, or mental faculties to prevent a rollback on inclines.
In an effort to prevent rollbacks, some prior artisans crafted wheelchairs with wheel locks for locking the large, rear wheels against rotation. With these prior art devices, a wheel lock assembly is typically mounted to the frame of the wheelchair adjacent each rear wheel. Each wheel lock assembly includes a hand-operated lever which is connected by mechanical means to a braking member for engaging the tire tread at the periphery of the wheel. Accordingly, when the lever is disposed in a free wheeling position, the braking member is spaced away from the wheel and the tire so as to allow the wheel to rotate freely. Likewise, when the handle is moved to the locked position, the brake member is moved into contact with the tire with sufficient force so as to press into, and temporarily deform, the outer surface of the tire to frictionally hinder rotation of the tire.
One of the drawbacks with these prior art rear wheel locks is that they require either a large manual effort or a long throw to lock the wheels from further rotation. Another drawback of these prior art devices is that the braking mechanism prevents any rotation of the tires in either direction. As will be appreciated, it is desirable at times to allow the wheels to move in the ascending direction while inhibiting movement in the descending direction, such as with a patient being transported or ascending an incline. For example, if the operator were to stop propelling the wheelchair up a hill and relax, gravity would urge the chair to roll backwards. Similarly, if the occupant removed his hands from the wheels to push open a door, the pushing tends to force the wheelchair in the opposite direction. This is true even with automatic doors, wherein the occupant is forced to press against a button to actuate the door. Oftentimes, an occupant must engage the brake to prevent a rollback when pressing the open button for a door; and unfortunately, by the time the occupant disengages the brake to egress through the door, the door would close again.
Accordingly, it is desirable to provide a one-way braking mechanism to provide for rotation of the wheels in only the forward direction. In an effort to meet this need, some prior artisans crafted “hill holder” mechanisms, or one-way clutches, to attach to the hub of the rear wheels. These prior art clutches are relatively expensive and mechanically complex. Other hill holders have been devised which also incorporate a wheel lock assembly. However, these combination devices suffer from numerous drawbacks as well. For example, U.S. Pat. No. 4,887,830 to Frough et al discloses a wheelchair with a combined wheel lock and hill holder. The device uses a cam to engage the brake. However, the device is spring loaded and must thus be manually engaged and disengaged. Once engaged, the wheelchair is hindered from movement in the rearward direction completely. Furthermore, once engaged, the drag of the device on a user's forward motion remains a noted drawback.
More significantly, with these prior art wheelchairs, the braking device needs to be disengaged anytime the wheels are to be rolled in the rearward direction. The constant burden of manually engaging and disengaging a device depending on whether the occupant is on level ground or desires to move rearwardly is a significant drawback to such devices. As will be appreciated, for wheelchair occupants of limited cognitive ability, upper body strength, dexterity, range of motion, coordination, or the like, manually engaging and disengaging a safety device is not a viable option.
One particularly advantageous braking system for overcoming the problems and drawbacks associated with prior art rollback prevention systems was described by the present inventor in co-pending U.S. Ser. No. 10/425,034, filed Apr. 29, 2003, entitled “Gravity Reacting Anti-Rollback Brake.” For example, as set forth in the application, a preferred embodiment of the Gravity Reacting Anti-Rollback Brake system, or “GRAB” system, comprises a pair of graded brake cam structures disposed on opposite ends of a connecting rod. The connecting rod and cams are operatively disposed adjacent the back wheels of a wheelchair via a lever assembly mount. The natural pull of gravity and the configuration of the cams operate to allow passage of wheels in both directions when on flat surfaces and in only a single direction when on an incline. Specifically, when on an incline, gravity operates to dispose cams relative to the wheels such that rotation of the wheels in one direction is hindered by a thickening of the cam body caused by rotation of the cam about its axis. The system also includes an adjustment mechanism for setting the incline angle at which the cams will operate to stop wheel rotation in the undesired direction.
While the GRAB system poses a novel and advantageous apparatus for dealing with the problem of rollback with wheelchair devices and the like, it will be appreciated that there are times when it would be advantageous for controlling the speed and movement of a wheelchair or other wheeled craft or device when descending an incline in the forward direction.
To exemplify the long-felt need in the art, consider electric wheelchairs for instance. Electric wheelchairs not only provide users with powered movement, but also provide automatic braking. Thus, electric wheelchairs inherently prevent unwanted rollback and govern forward speed on inclines or slopes regardless of the weight, strength or endurance of the user. By contrast, manually powered wheelchairs do not. Manually powered wheelchairs require a constant force grip that is affected by the weight, strength and endurance of the operator. Not all wheelchair users need the assistance of an electric wheelchair because these individuals have sufficient strength and dexterity to propel and navigate themselves. However, all wheelchair users can benefit from automatic assisted braking when descending a steep hill. Accordingly, without a braking system, manual wheelchair users attempting to navigate a hilly or steep terrain are at a disadvantage to an electric wheelchair user. Thus, paradoxically, users not requiring the assistance of an electric wheelchair find their community mobility more compromised than those in need of an electric wheelchair.
The forgoing underscores some of the problems associated with prior art braking systems. Furthermore, the foregoing highlights the long-felt, yet unresolved need in the art for a wheelchair “hybrid” to span the huge gap between manual and electric wheelchairs in regards to cost and function. Moreover, the foregoing highlights the need in the art for a braking system which automatically engages and disengages based on the user's terrain. The foregoing also highlights the need in the art for a manual wheelchair providing automatic and/or selectively automatic braking when ascending and descending graded terrain.